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The effect of feeding willow upon the death of established parasites and upon parasite fecundity : a thesis presented in partial fulfilment of the requirements for the degree of Animal Science at Massey University, Palmerston North, New Zealand

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Abstract

Two indoor feeding experiments were conducted at the Animal Physiology Unit
(APU) of Massey University, involving young sheep, to investigate the effect of
feeding forage willow upon the death of established parasites and upon parasite
fecundity, using chaffed lucerne as the control diet.
Experiment 1: Twenty-four (24) parasite-free weaned hoggets weighing 29.9 ±1.2 kg
(SD) were individually penned and fed chaffed lucerne ad libitum during a preexperimental
adaption period of 5 weeks. They were then fed either lucerne chaff or
chopped willow for a further 5 weeks (n = 12/group) and intakes were adjusted such
that the DMI of the two groups was similar during weeks 9 & 10. All lambs were
infected with L3 larvae parasites comprising 20,650 Teladorsagia, 1,320
Trichostrongylus and 330 Cooperia through oral drenching 12 days before willow
feeding started. This was done after confirmation that the sheep were free of
nematodes through FEC analysis. Total faeces were collected for 3 day periods
towards the end of weeks 9 & 10, to measure diet digestibility and total faecal egg
excretion. The sheep were slaughtered at the end of week 10. Voluntary feed intake
(VFI), FEC and liveweight were measured weekly, whilst burdens of individual
parasites and carcass characteristics were measured after slaughter. Duplicate samples
of each feed offered and individual animal refusals were taken daily and pooled
weekly per animal for chemical analysis. Female worm fecundity was calculated by
two methods. Blood samples for immunological analysis were collected on days 20,
34, 51 and 70, and analysed for components of white blood cells (WBC) and for
lymphocyte subsets.
Experiment 2: A 2 x 2 changeover experiment was conducted, involving two time
periods (Period 1 and Period 2 each of 14 days) with the same diets as used in
Experiment 1, fed to 9 individually penned parasite-free young sheep randomly
allocated to experimental diets. The parameters investigated were FEC and larvae
hatching. Initially, a period of 7 days was allowed for acclimatisation in which both
groups were fed on half willow and half lucerne chaff. This was followed by Period 1
with 4 lambs fed lucerne and 5 fed willow, after which the diets were changed over
for Period 2. Total faeces produced were collected from all animals on the last day of
each period using bagged sheep. A known number of Teladorsagia eggs (500 epg)
was then added to faecal samples from these sheep and faeces-egg mixtures were
made from which FEC was determined, to see if egg recovery was affected by these
diets. Faecal samples for Period 2 with added eggs were also incubated for 10 days to
measure hatchability.
The recovery of added Teladorsagia eggs in Experiment 2 was 85% in lucerne-fed
lambs and 53% willow-fed lambs (P<0.001); these were used as correction factors for
Experiment 1 data. Larvae that hatched per gram of wet faeces in Experiment 2
tended to be lower for sheep fed willow than lucerne chaff (71% vs 83% of eggs
added; P=0.08).
Willow feed offered had lower DM (P<0.001) and CP (P<0.05) content, but had a
significantly higher OM content (P<0.01) than lucerne chaff. Condensed tannin
content of chopped willow was 27 g/kg DM, with only traces for lucerne. Apparent
digestibility for DM (62.4% vs 59.5%; P≤0.05), OM (64.8% vs 59.9%; P≤0.001),
DOMD (58.1% vs 55.0%; P≤0.01) and calculated ME (9.48 MJ/kg vs 8.96 MJ/kg;
P≤0.01) were higher for the willow diet. VFI was similar for both groups during the
adaption period (P>0.05) but declined with the introduction of willow in week 6
(P<0.001) and then progressively increased until it was similar to lucerne-fed sheep in
weeks 9 & 10 (P>0.05). Calculated DM intake per head/day during the last two weeks
of Experiment 1 was similar for the two groups (P>0.05); while the willow group had
higher ME (P<0.01) and CP (P<0.001) intake per animal/day. Liveweight increased
for the two groups during the adaption period (P>0.05), then declined for willow-fed
lambs in week 6 (P<0.001) but later increased and by week 10 was similar to that of
lucerne-fed lambs. The willow-fed lambs had lower carcass GR than the lucerne-fed
lambs (P<0.01) when carcass weight was used as a covariate. Adjusted total daily egg
production in Experiment 1 was lower in willow-fed sheep than lucerne-fed sheep,
due to reductions for Haemonchus spp. (P<0.05) and Teladorsagia spp. (P<0.05). The
per capita fecundity for Haemonchus worm spp. (P<0.05) and the in utero fecundity
in both abomasal Teladorsagia spp. and small intestinal Trichostrongylus spp.
(P<0.001) were lower for willow-fed sheep. There was reduced production of larvae
for both Haemonchus spp. and Teladorsagia spp. (P<0.05) in willow-fed sheep.
Feeding willow reduced the burden of Haemonchus adult worms in the abomasum
(P<0.01) but reduced female worm burden only in Teladorsagia spp. (P<0.05) and
reduced Cooperia spp. in the small intestines (P<0.01). Total WBC, total
lymphocytes, subsets of lymphocytes and other white-cell groups were not affected by
willow feeding (P>0.1).
It was concluded that feeding chopped willow to young sheep reduced nematode
worm burdens in the abomasum, especially both male and female Haemonchus spp.,
and reduced female worm burdens of Teladorsagia spp. Female worm fecundity of
both species was also reduced by willow feeding. These reductions have been
associated with CT content in the willow feed and the reduced worm burdens have
been attributed to the death of the established worms by CT, since there was no
evidence of immune priming in willow-fed sheep. Compounds present in the faeces of
willow-fed sheep have been found to mask some of the nematode eggs, making them
invisible by microscopic examination while keeping their viability. It is postulated
that this could be due to binding of nematode eggs to insoluble CT associated with
indigestible fibre in the faeces of willow-fed sheep. Conventional methods of
measuring FEC therefore underestimated nematode eggs present in the faeces of
willow-fed sheep and this needs to be checked for other CT-containing forages.